The objectives of this core are to provide high quality pathologic services and in vivo tumor and xenograft models for biologic studies of breast tumor biology and experimental therapeutics. To this end, the following specific aims are proposed. 1) Provide a source of well characterized human breast tumor xenografts for translational studies within the program. Assist in the conduct and analysis of such studies. 2) Develop additional xenograft lines, as dictated by needs of the program. 3) Provide support and expertise in the maintenance and operation of the Laser Capture Microdissection microscope system and other routine immunohistochemical and in situ hybridization studies. 4) A long term goal is to provide comprehensive banks of pre-treatment plasma and frozen and paraffin embedded tissues that are well characterized in terms of fidelity of cancer in tissue samples and as well as being tied to information regarding the staging, treatment history and response of each patient. Specific project collaborations have been established and additional collaborative studies are planned that use this Core facility.